JP Morgan has hinted it could quit the UK if Britain votes to leave the EU as US investment banks line up to support the In campaign.

The bank’s chief executive Jamie Dimon said: “Britain’s been a great home for financial companies and [EU membership] has benefited London quite a bit. We’d like to stay there, but we if can’t, we can’t.”

JP Morgan employs about 19,000 people in the UK, with its main offices in Canary Wharf, Bournemouth and Glasgow. The bank employs Tony Blair as an adviser.

Dimon was speaking on the sidelines of the annual world economic forum in Davos as it emerged that JP Morgan, which is America’s biggest bank, is offering financial support to the Britain Stronger in Europe campaign.

On Wednesday it was revealed that Goldman Sachs has also pledged several hundred thousand pounds to the campaign.

Dimon’s suggestion that JP Morgan might quit the UK came as David Cameron prepared to call on business chiefs to support him in keeping Britain in the 28-member union.

The bank chief refused to detail the exact scale of JP Morgan’s donation to the In campaign but it is likely to be a significant sum of money. He said: “We’ve just starting doing (it)… Wish we didn’t have to do it at all.” He added: “I can’t tell the British people what to do, it’s up to them.”

“This is a once-in-a-generation moment and the stakes are high,” he said. “If you want a more competitive Europe, where the single market is completed, where there are more trade deals and fewer regulations: join me in making that case.

“If you believe, like I do, that Britain is better off in a reformed European Union, then, when the time comes, help me make that case for Britain to stay.”

The future of Europe has already been debated among the 2,000 delegates to the annual gathering in the Swiss Alpine ski resort. Cameron is thought to want to hold the referendum in June to avoid prolonged coverage of refugees fleeing into the EU.

The French prime minister, Manual Valls said it would be a “tragedy for Europe” if the UK electorate voted to leave. He added that he thought unlikely Cameron could reach a new deal with Europe at a planned summit in February.

Valls said: “We must find a compromise, and everyone must contribute to it.”